Dark blood delayed enhancement magnetic resonance viability imaging techniques for assessing subendocardial infarcts

ABSTRACT

The technology herein provides a dark blood delayed enhancement technique that improves the visualization of subendocardial infarcts that may otherwise be disguised by the bright blood pool. The timed combination of a slice-selective and a non-selective preparation improves the infarct/blood contrast by decoupling their relaxation curves thereby nulling both the blood and the non-infarcted myocardium. This causes the infarct to be imaged bright and the blood and non-infarct to both be imaged dark. The slice-selective preparation occurs early enough in the cardiac cycle so that fresh blood can enter the imaged slice.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/957,520filed Dec. 17, 2007, now U.S. Pat. No. 8,086,297, which applicationclaims the benefit of priority from provisional application No.60/887,596 filed Jan. 31, 2007. Each of these prior disclosures isincorporated herein by reference

TECHNOLOGICAL FIELD

The technology herein relates to magnetic resonance imaging (MRI) pulsesequences for use in detecting infarct (dead heart cells or scars) inthe human heart, and more particularly to black blood viability magneticresonance imaging (MRI) techniques that render blood and non-infarctedmyocardium dark and infarct bright.

BACKGROUND AND SUMMARY

Myocardial infarction (MI) occurs in almost a million people each yearin the United States, where coronary heart disease is the leading causeof hospital admissions. According to the joint American College ofCardiology and European Society of Cardiology consensus documentconcerning the redefinition of MI, the diagnosis of MI is often based oncardiac biomarkers and ECG changes. However, biomarkers are onlyelevated for 4 to 10 days after an acute event. Thus, biomarkers are notuseful for the diagnosis of subacute or chronic MI. The ECG also haslimitations: Q waves that form the fundamental basis of the diagnosis ofchronic MI may be absent or, if initially present, may disappear at alater time point.

Cardiovascular magnetic resonance (CMR) imaging is a highly attractivemodality for the assessment of myocardial infarction and viabilitybecause of high spatial resolution and accuracy. However, practicaldrawbacks have in the past limited the impact of such technology forgeneral clinical use. For example, standard CMR is generally morecomplex as compared to some imaging modalities. Patient and protocolsetup times have been generally longer, and multiple breath-holds andlonger scanning times have been necessary. These conditions can limitclinical throughput and the types of patients that can be scanned, andmay also increase the complexity and length of CMR training.

In view of the importance of this area of investigation to societalhealth, much work has been done in the past to develop imagingtechniques capable of detecting infarcts and determining viability.

For example, work at Northwestern University by Dr. Raymond J. Kim andothers resulted in U.S. Pat. No. 6,205,349 entitled “Differentiatingnormal living myocardial tissue, injured living myocardial tissue, andinfarcted myocardial tissue in vivo using magnetic resonance imaging”,describing techniques for distinguishing between normal, injured butliving, and infarcted myocardium using MR imaging. Because they solvemany of the challenges described above, such delayedcontrast-enhancement CMR techniques have become the gold standard forimaging myocardial infarction. Such delayed enhancement images exhibitexcellent contrast between normal and infracted myocardium due tonulling of normal myocardium. The current clinical standard is aso-called segmented IR-Turbo Flash technology that acquires data duringa breath hold of typically 10 seconds or less. Furthermore, using suchdelayed contrast enhancement techniques, myocardial infarction can bedetected rapidly by subsecond delayed contrast-enhancement CMR duringfree breathing with high accuracy. The clinical implication is thatdelayed contrast-enhancement CMR can approach a quick “push-button”technique with the ability to scan a wide range of patients, includingthose who are more acutely ill, those with dyspnea, or those unable toundergo a prolonged examination. Moreover, clinical throughput could beincreased multifold. See e.g., Sievers et al, “Rapid Detection ofMyocardial Infarction by Subsecond, Free-Breathing DelayedContrast-Enhancement Cardiovascular Magnetic Resonance”, Circulation2007;115;236-244 and other articles by Drs. Kim, Judd and/or Rehwald.

Such known prior art delayed enhancement MRI pulse sequences can deliverimages in which viable myocardium (living heart tissue) appears dark andinfarct and blood appears bright. For example, a frequently used exam incardiovascular MRI is called “viability imaging” or “myocardial delayedenhancement.” For this test, a MR contrast agent is injected into thepatient intravenously while the patient is lying in the MRI scanner.After about 10 minutes, the contrast agent has distributed throughoutthe patient's body including the heart. In the heart, this agentaccumulates primarily in dead heart cells and in scar, both known asinfarcted territory (such cells have died e.g., due to a prior heartattack—infarct). As the contrast agent regionally alters the magneticproperties of the heart tissue and as it primarily accumulates in thedead cells, it is possible to visualize regions of dead cells with MRI.

One so-called “pulse sequence” provided by software running on a MRIscanner that can be used to provide such imaging is called InversionRecovery Turbo Fast Low Angle Shot (IR—TurboFlash). This is the vendoracronym of Siemens Medical Solutions. Other vendors such as GE MedicalSystems and Philips have similar products with different acronyms. Suchmethods reliably deliver images in which viable myocardium (living heartcells) appears dark, and infarct (dead heart cells or scar) and bloodappear bright.

Such techniques as described above are sufficient in many cases todetect infarcts and help physicians determine myocardial viability. Forexample, the identification of large areas of dysfunctional but viablemyocardium predicts situations where revascularization is likely toimprove functional class, augment regional and global LVEF and increasesurvival. Conversely, the presence of predominant myocardial scarringpredicts increased operative mortality and the absence of these salutaryeffects.

While such “bright blood” imaging and analysis techniques have beensuccessful, it has become evident that in patients with smallsubendocardial infarcts (infarcts located at the inner side of the heartwall adjacent to the blood pool), the bright blood can sometimes obscurethe bright infarct. Small subendocardial infarcts are sometimesdifficult to detect as they may have a similar signal intensity (T1values) as the blood pool. Therefore, small subendocardial infarcts areoften hard to detect in standard delayed enhancement images. The infarctmay be missed or its size may be underestimated. Ideally, a viabilitysequence would have excellent contrast between infarct and both normalmyocardium and the blood pool. Techniques providing images in whichblood appears dark/black while leaving the infarct bright and normalmyocardium dark have been highly sought after.

So-called “dark blood” or “black blood” angiography MRI pulse sequencesare known. Such techniques make flowing blood appear dark or black inthe image and make stationary blood or tissue appear to be bright in theimage. In one such type of “black blood” pulse sequence, early echoesare more heavily proton density weighted than later echoes (the laterechoes can be more T2 weighted). Depending on the exact sequenceimplementation, the obtained images can be more proton-weighted or moreT2-weighted.

Also, the idea of combining a slice-selective with a non-selectiveinversion pulse has been used for several years for acquiringblack-blood images. However, generally the two pulses are playedimmediately after one another. A known technique called “Black-BloodHASTE” is usually used without the presence of contrast agent in theblood pool, and it only nulls (makes black) blood, not normalmyocardium.

For example, it is generally known that nulling two T1-species can beachieved by a timed combination of two non-selective inversion pulses.However, due to their similar T1 values, the contrast between infarctand blood is still small.

Additionally, techniques are known that decouple blood preparation fromtissue preparation by use of a non-selective inversion followed by aslice-selective “re-inversion” followed by image acquisition (“BlackBlood HASTE”). Such techniques work well because there is sufficienttime for blood exchange and preparation and readout occur when the heartis in nearly the same position (before contraction and during mid tolate diastole, respectively). However, a recurring problem has been thatthe standard classic double-inversion “dark blood” approach does notwork in conjunction with delayed enhancement since the contrast agent ispresent and since only one T1 species is nulled and so cannot be usedfor viability imaging without adding further preparation pulses. Thereare therefore challenges associated with using the classic approachesfor dark blood viability. For example, the classic dark bloodpreparation does not provide T1-weighting of the tissue. An additionalIR pulse would need to be played before or after to double-IR dark bloodpreparation to get dark blood delayed enhancement images. Generally, thesimultaneous nulling of blood and normal myocardium would be extremelydifficult as there may be insufficient blood exchange between double IRpreparation and image readout.

Dark blood delayed enhancement techniques that could image blood andnormal myocardium as dark/black while leaving the infarct bright wouldbe clinically useful. For example, it would be desirable to providetechniques which would:

-   -   Null blood and normal myocardium at the time of readout;    -   Play slice-selective preparation before systolic contraction        (blood exchange, slice position);    -   Provide image readout late enough (blood exchange, similar slice        position as during slice-selective preparation); and    -   Allow a non-selective preparation to be played out at any time.

The idea of nulling more than one type of tissue per se is known.However, to our knowledge, it has not generally been used in acombination of early slice-selective preparation, blood exchange of theheart, and late non-selective preparation in the presence of MR-contrastagent to acquire “black-blood viability” images (note that in thiscontext, “viability” refers to the property of heart tissue, myocardium,of being alive, “viable”, or dead, “non-viable”).

We have now developed a new “dark blood” or “black blood” myocardialviability delayed enhancement imaging technique which can obtain darkblood delayed enhancement images by a timed combination of a selectivepreparation after the cardial R-wave and a later, non-selectiveinversion. Such MRI sequences can aid the detection of smallsubendocardial infarcts.

One exemplary illustrative non-limiting implementation combines an earlyslice-selective magnetic preparation of heart tissue, followed by aparticular calculated delay to allow blood exchange of the heart,followed by late non-selective inversion (e.g., in the followingheartbeat). The timed combination of slice-selective and non-selectivepreparation decouples the infarct-curve from the blood-curve and enablesgreater image contrast than is possible for example using twonon-selective preparations.

In one exemplary illustrative non-limiting implementation, to make bothblood and non-infarcted myocardium appear black in the image, apreparation is used to cause the relaxation curves of both T1-species tosimultaneously cross the zero-line (“be nulled”). In one exemplaryillustrative non-limiting implementation, the timed combination ofslice-selective and non-selective preparation decouples the infarct fromthe blood curve and enables good image contrast.

In one exemplary illustrative non-limiting implementation, the time fromthe nsIR (non-selective inversion recovery) to the center of K-space ischosen to null blood and only depends on its T1. The time between theSSSR (slice-selective saturation recovery) pulse and nsIR pulse is setto null normal myocardium when blood is nulled.

In one exemplary illustrative non-limiting implementation, contrastbetween infarct and blood is improved at the expense of a lower infarctsignal-to-noise ratio. Gradient, turbo-spin echo (tse) and SSFP readoutscan be used. The tse readout results in a high signal to noise ratio andbetter blood nulling.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will be better and morecompletely understood by referring to the following detailed descriptionof exemplary non-limiting illustrative embodiments in conjunction withthe drawings of which:

FIG. 1 shows an example a cardial MRI system;

FIGS. 2A and 2B show example relaxation curves;

FIG. 2C shows exemplary illustrative non-limiting partial inversionblack blood viability sequences;

FIG. 2D shows example slice-selective preparation and blood-exchange anddata readout during mid to late diastole;

FIG. 2E shows an exemplary illustrative non-limiting user interfacescreen;

FIG. 3 shows an exemplary illustrative non-limiting preparationincluding slice-selective saturation and non-selective inversion;

FIG. 3A shows an exemplary illustrative non-limiting slice-selectivesaturation and non-selective inversion pulse sequence;

FIG. 3B shows exemplary illustrative non-limiting magnetizationscorresponding to FIGS. 3 & 3A;

FIGS. 3C-1 & 3C-2 show exemplary illustrative non-limiting comparisonimages;

FIG. 4 shows an exemplary illustrative non-limiting preparationincluding slice-selective inversion and non-selective inversion;

FIG. 4A shows an exemplary illustrative non-limiting slice-selectiveinversion and non-selective inversion pulse sequence;

FIG. 4B shows exemplary illustrative non-limiting magnetizationscorresponding to FIGS. 4 & 4A;

FIGS. 4C-1 and 4C-2 show exemplary illustrative non-limiting comparisonimages;

FIGS. 5A, 5B and 5C show images developed using standard “bright blood”,IRIR Gradient Echo (GRE) “black blood” and IRIR Turbo Spin Echo (TSE)“black blood” readouts, respectively;

FIG. 6 shows a further exemplary illustrative non-limiting preparationincluding a partial selective inversion followed by a non-selectiveinversion;

FIG. 7 presents another exemplary illustrative non-limiting preparationincluding two selective inversions and a non-selective inversion;

FIG. 8 shows an exemplary illustrative pulse sequence corresponding toFIG. 7;

FIG. 9 shows an exemplary illustrative non-limiting preparationincluding a non-selective inversion followed by a timed classic doubleinversion;

FIG. 10 shows an exemplary illustrative non-limiting preparationincluding a slice-selective inversion followed by a timed classic doubleinversion;

FIGS. 11A, 12A, 13A and 14A show example infarcted dog heart imagingresults without black blood preparation techniques;

FIGS. 11B, 12B,13B and 14B show example infarcted dog heart imagingresults using black blood preparation techniques;

FIGS. 15A and 16A show infarcted human heart imaging results imagesdeveloped using standard techniques;

FIGS. 15B and 16B show infarcted human heart imaging results developedusing black blood preparation and gradient echo readout; and

FIGS. 15C and 16C show infarcted human heart imaging results developedusing black blood preparation and Turbo spin echo readout.

DETAILED DESCRIPTION OF EXEMPLARY ILLUSTRATIVE NON-LIMITINGIMPLEMENTATIONS

The exemplary illustrative non-limiting technology herein can beimplemented on any commercial cardiac MRI scanner. No additionalhardware is required. FIG. 1 shows an example such magnetic resonanceimaging (“MRI”) system 10 including a data acquisition and displaycomputer 50 coupled to an operator console O, a MRI real-time controlsequencer 52, and a MRI subsystem 54. MRI subsystem 54 includes XYZmagnetic gradient coils and associated amplifiers 68, a static Z-axismagnet 69, a digital RF transmitter 62, a digital RF receiver 60, atransmit/receive switch 64, and RF coil(s) 66. As is well known, adedicated cardiac or torso phased-array coil is typically used forcardiac imaging. Electrocardiogram (ECG) leads L are used in cardiacimaging to synchronize control sequencer 52 with electrical stimulationof the heart by the brain.

One exemplary illustrative non-limiting implementation uses a clinicalMR scanner (Magnetom Sonata, Siemens Medical Solutions) set withparameters including field of view 300 mm, matrix 256×114, TE 3.85 ms,spatial resolution 1.6×1.6×6 mm, lines per segment 19, bandwidth 160Hz/pixel, acquisition duration 18 heartbeats. The timings specifiedherein are applicable to MRI scanners with 1.5 Tesla field strength, butthis is by way of example only. At higher Tesla field strengths, therelaxation time T1 increases and the time delays should be increasedaccordingly.

Subsystem 54 is controlled in real time by sequencer 52 to generatemagnetic and radio frequency fields that stimulate nuclear magneticresonance (“NMR”) phenomena in an object P (e.g., a human body) to beimaged. A suitable well known contrast agent (C) such as for example KgGd-DTPA is injected intravenously into the patient P in a well knownmanner. A resulting image of patient P on display 58 shows cardiacfeatures and structures that cannot be seen using X-ray, ultrasound orother medical imaging techniques. In the exemplary illustrativenon-limiting implementation, the resulting dark or black bloodmyocardial viability imaging shows blood and healthy myocardium as blackor dark and shows infarcts (including subendocardial infarcts) asbright.

Exemplary Techniques for Nulling Both Blood and Normal Myocardium

In one exemplary illustrative non-limiting implementation, we programthe control sequencer 52 of such conventional MRI equipment to generatea pulse sequence that combines an early slice-selective magneticpreparation of heart tissue followed by a later global (hereafterreferred to as “non-selective”) preparation. Unlike the traditional“black-blood” approaches, the preparations are not played back to backbut rather are planned with a calculated delay between them. The timedcombination of both preparations allows a subsequent readout process torender both normal myocardium and blood dark, and infarcted territorybright.

FIG. 2A shows relaxation curves for normal myocardium,—infarct, andblood about 15 minutes after IV injection of 0.125 mmol/Kg Gd-DTPAcontrast agent (T1 blood=330 ms, T1 normal=490 ms, T1 infarct=280 ms).As is well known, a contrast agent such as Gadolinium will tend toconcentrate in the infarcted myocardial tissue but not in healthy ornormal myocardium—allowing infarct myocardium and normal myocardium tobe distinguished and the normal myocardium to be nulled. However, as canbe seen in FIG. 2A, blood tends to exhibit nearly the same relaxationtime as infarct myocardium due to the contrast agent being present inthe blood pool and thus generates nearly the same signal—sometimesresulting in poor infarct/blood contrast.

Timing and relaxation curves for an exemplary illustrative non-limitingdouble-preparation pulse sequence consisting of a slice-selectivepreparation (in this case a slice-selective saturation (SSSR)) followedby a non-selective inversion (NSIR) are shown in FIG. 2B. The timedcombination of slice-selective and non-selective preparation decouplesthe infarct relaxation curve from the blood-curve and enables greaterimage contrast than is possible with two non-selective preparations. Thetime from the NSIR to the center of k-space is chosen to null blood anddepends only on its T1. The time between the SSSR and NSIR pulse is setto null normal myocardium at the same time blood is nulled.

Exemplary Illustrative Non-Limiting NMR Pulse Sequences

FIG. 2C shows an exemplary illustrative non-limiting black bloodviability MRI sequence based on the FIG. 2B approach but the sliceselective pulse is a partial inversion pulse and not a saturation pulsewhich does not affect the concept but lengthens the timing between sliceselective and non-selective preparation. FIG. 2D shows an exemplaryillustrative non-limiting series of diagrams illustrating correspondingslice-selective preparation and blood exchange within the heart.

As shown in FIG. 2C, prior to systole (i.e., after R-wave or duringprevious heartbeat), sequencer 52 controls the MRI subsystem 54 togenerate a first preparation slice-selective partial inversion RF pulsewithin a particular slice of the heart. The slice-selective preparationis done at any time during one heartbeat or soon after the R-wave of thefollowing, before cardiac contraction starts (see panel A of FIG. 2D).

This first, slice-selective preparation causes the magnetizationorientation of the spin axes within the myocardium within the slice toat least partially invert. As soon as the RF pulse ends, the protonswithin the myocardium begin to relax. As is well known, the contrastagent modifies the proton relaxation times of the infarct myocardium inwhich it is concentrated. Therefore, the normal and infarct myocardiumrelax at different rates (in this example, the infarct protons relax andreturn to steady state more rapidly due to the presence of the contrastagent).

The sequencer 52 then controls—at an appropriate timing—the MRIsubsystem 54 to generate a further preparation RF pulse in the form of anon-selective inversion RF pulse during the following heartbeat. At thispoint in time, the heart has entered its systolic phase and theventricles have contracted to drive blood through the aorta andpulmonary artery (see FIG. 2D, panel B). Blood that has seen the earlyslice-selective preparation is thus expelled from the slice (panel B).Therefore, the blood previously prepared by the first slice-selectivepartial inversion RF pulse is mostly no longer within the heart (havingbeen expelled during systole).

This second, global inversion preparation, being non-selective, isapplied to all tissue in the heart as well as to all blood in and nearthe heart. This non-selective inversion RF pulse causes themagnetization (orientation) of the proton spin axes within all relevantstructures (normal myocardium, infarct myocardium and blood) to invert.However, due to the previous slice-selective preparation which preparedthe myocardium but not the blood, the relaxation of each of the threestructure categories (blood, normal myocardium, andcontrast-concentrated infarct myocardium) begins at differentmagnetizations as shown in FIG. 2C. Furthermore, since the blood protonsand the normal myocardium protons have different relaxation rates, theirrelaxation curves intersect at a point X at a particular point in timet—and the relaxation curve of the infarct protons (which are relaxing ata still different rate) does not intersect at this same point X.

In the exemplary illustrative non-limiting implementation, data readouttakes place during the diastolic phase (FIG. 2D panel C) when new bloodhas begun to fill the heart. The protons within this new blood have notbeen prepared by the previous slice-selective preparation pulse becausethey were not within the slice previously prepared by theslice-selective partial inversion. During data readout, only blood thathas experienced the late non-selective preparation (but not the earlyslice-selective preparation) is present in the slice. Preparation ofheart tissue and blood are thus decoupled. In the exemplary illustrativenon-limiting implementation, the non-selective pulse can come before allselectively excited blood has been expelled so long as substantially allselectively excited blood has been expelled at the time of readout.

By timing readout appropriately based on the intersection of therelaxation curves, we have the opportunity to null both the unpreparedblood protons and the normal myocardium protons (to provide dark orblack portions of the image) while enhancing the portions of the imagecorresponding to myocardium infarct (so that those image portions appearbright).

FIG. 2E shows an exemplary illustrative non-limiting implementation of auser interface that may be displayed on the operator console O toprovide the FIG. 2C pulse sequence. This exemplary screen shows inputboxes for the inversion times T1 for normal (living) myocardium andblood. It also shows thickness of the preparation slice in % whichusually does not need to be adjusted. Using these simple parameters in aclinical setting, the MRI operator can control the quality of theimaging results using the exemplary illustrative non-limitingimplementation. In general, adjusting the timing between all preparationpulses and the readout module can be time-consuming. To simplify theoperation of the sequences for the user, in one exemplary illustrativenon-limiting implementation, the timing is automatically calculated bythe user interface of the sequence. The user still needs to know therelaxation times of “normal myocardium” and blood, but the timing isthen calculated based on these provided numbers. Different formulas areused for each method.

Example Preparation: Selective Saturation Followed by Non-SelectiveInversion

FIG. 3 shows the magnetization recovery of normal myocardium, infarct,and blood as occurring in an exemplary illustrative non-limitingimplementation providing a slice-selective saturation pulse (SS SR)followed by a non-selective inversion. The curves shown are for typicalrelaxation constants (T1-valued) 10-20 minutes after an administrationof a 1.25 mmol/Kg dose of contrast agent. The T1-values used in this andthe following simulations are T1 infarct=280 ms, T1 normal=490 ms, andT1 blood=330 ms. These values change as a function of time aftercontrast agent injection, and modify the timing of the pulses needed tomake blood and normal myocardium black.

In this particular non-limiting illustrative implementation, theslice-selective saturation recovery pulse (SS SR) sets the magnetizationof infarct and “normal” to zero. The magnetization of both tissue typesrecover and is experiencing a non-selective inversion recovery pulse (NSIR) 440 ms later. The inverted magnetizations continue to recover, nowfrom different starting points. The magnetization of “new” blood (i.e,.blood that was not within the heart during the first preparation) thatwas unaffected by the SS SR pulse is now inverted and recovers as well,starting from −M0. Due to the time between both preparations, the bloodand the “normal” curve cross zero at the same time. If data is acquiredat that time, they do not yield any signal (they have no magnetization)and thus appear black. “Infarct” has positive magnetization giving riseto a bright signal in the resulting image.

FIG. 3A shows an example pulse sequence to accomplish the methoddescribed above in connection with FIG. 3. Note the two preparationpulses (a slice-selective saturation pulse followed by a non-selectiveinversion pulse). Conventional readout pulses follow.

FIG. 3B shows how slice-selective saturation and non-selectivepreparation affect magnetization. The first panel (all the way to theleft) shows magnetization vectors for infarct, blood and normalmyocardium all at +M0. An infarct region is marked by a dotted whiteline and two “normal” regions are delineated by a dotted black line.

The slice-selective saturation preparation shown in the FIG. 3B secondpanel erases the magnetization in the slice. The magnetization in theslice then recovers to different values depending on the tissue type(see center panel 3). After the following non-selective inversionpreparation in panel 4, blood magnetization is at −M0, and “normal” andinfarct are between −M0 and zero. “Normal” is closer to zero, but willrecover slower than infarct.

At the time of data readout (right hand panel 5), magnetization of bloodand normal myocardium have both recovered to zero, but they did so fromdifferent starting points and with different speed. Infarct has fasterrecovery and has positive magnetization at that time.

FIG. 3C-2 shows an example image obtained from the above-describedpreparation using selective saturation followed by non-selectiveinversion. As compared to FIG. 3C-1 (current standard of clinicalpractice NSIR), one can see that the FIG. 3C-2 image allows the brightinfarct to be more clearly seen because it is not obscured by brightsurrounding blood.

Example Selective Inversion Followed by Non-Selective Inversion

FIG. 4 shows an exemplary illustrative non-limiting implementationwherein the first preparation is a slice-selective inversion (SSIR)rather than a slice-selective saturation. Using a slice-selectiveinversion pulse allows a longer time between slice-selective preparationand data readout. More blood exchange can take place—making the methodmore robust to slow blood flow (which often occurs in patients withinfarcts) and more user-friendly. A potential disadvantage is a lowersignal from the infarct, leading to noisier images (more speckles).

FIG. 4A shows a corresponding exemplary pulse sequence. Note the first,slice-selective inversion preparation RF pulse followed by anon-selective inversion RF pulse.

FIG. 4B shows how slice-selective inversion and non-selectivepreparation affect magnetization during the FIG. 4B sequence. The first(left-most) panel shows magnetization vectors all at +M0. As describedabove in connection with FIG. 3B, an infarct region is marked by adotted line, two “normal” regions by a dotted black line.

The slice-selective inversion preparation shown in panel 2 inverts themagnetization in the slice. The magnetization in the slice then recoversto different values depending on the tissue type (panel 3). After thesecond preparation pulse (non-selective inversion) in panel 4, bloodmagnetization is at −M0, and “normal” and infarct are between −M0 andzero. “Normal” is closer to zero, but will recover slower than infarct.At the time of data readout magnetization of blood normal myocardiumhave both recovered to zero, but they did so from different startingpoints and with different speed. Infarct has faster recovery and haspositive magnetization at that time.

FIG. 4C-2 shows an example image obtained from the above-describedpreparation using selective saturation followed by non-selectiveinversion. As compared to FIG. 4C-1 (current standard of clinicalpractice NSIR), one can see that the FIG. 4C-2 image allows the brightinfarct to be more clearly seen because it is not obscured by brightsurrounding blood.

Exemplary Readout Techniques

The exemplary pulse sequences described above make use of conventionalreadout sequences. Two common readout sequences are the so- called“gradient echo” (GRE) readout and the “Turbo Spin Echo (TSE). Any otherpulse sequence readout technique may be used such as steady state freeprecession (SSFP) also known under the vendor acronyms True Fisp(Siemens) and FIESTA (GE). FIGS. 5A, 5B and 5C show a comparison of thestandard (bright-blood) technique on the left, the black blood with GREin the center, and the black blood with TSE readout on the right. Thehigher signal of the latter (less speckles) can be seen.

Example Partial Selective Inversion Followed by Non-Selective Inversion

FIG. 6 shows a further exemplary illustrative non-limitingimplementation using a preparation consisting of a partial selectiveinversion followed by a non-selective inversion. A partial selectiveinversion or saturation (by way of example, a 50% inversion is shown inFIG. 6) allows modifying the time delay between first and secondpreparation event by varying the degree of inversion or saturation. Theshortest delay is obtained with a partial saturation, the longest withan inversion pulse. An advantage of this implementation is that byvarying the degree of saturation or inversion, the timing can beadjusted so that the slice selective preparation always occurs rightafter the R-wave, and the readout in mid to late diastole, irrespectiveof the heartbeat duration. These are the best locations for preparationand data readout which may not be obtained due to timing requirementsconflicting with the length of a heartbeat.

Example Two Selective Inversions Followed by Non-Selective Inversion

FIG. 7 presents another variation on the idea of making both blood and“normal” dark at the same time. In this exemplary illustrativenon-limiting implementation, two SS IR pulses are followed by a NS IRpulse. FIG. 8 shows a corresponding exemplary pulse sequence. Anadvantage of this method is improved signal of the infarct. Adisadvantage is the need to adjust two time delays instead of one, whichreduces its ease of use. This could be overcome with timing calculationsimplemented in the user interface.

Example Non-Selective IR Followed by Timed Classic Double IR

FIGS. 9 and 10 show additional exemplary illustrative non-limitingimplementations providing triple inversion recovery “triple IR” typepreparation schemes. The T1-values used in the recovery curvessimulations in FIGS. 9 and 10 are T1 infarct=280 ms, T1 normal=490 ms,and T1 blood=330 ms in this particular example.

In the exemplary illustrative non-implementations shown in FIGS. 9 and10, a preparation pulse is played at the beginning of the preparationscheme and is later followed by a so-called double-IR preparation. Thetime between the first preparation and the double-IR preparation is ofthe essence. The combination of a preparation, an exact time delay, andthis classic DIR provides useful results.

The double-IR preparation is widely used in MRI. We will refer to it as“classic double IR or classic DIR”. This classic DIR preparationconsists of a non-selective inversion immediately followed by aslice-selective inversion. Therefore, the slice seeing this preparationis untouched (inverted, then immediately re-inverted) whereas the bloodand tissue outside the slice is inverted. Later, at the time of datareadout, the outside (inverted) blood has entered the slice and isdifferently prepared than the slice itself. For our dark blood purposes,playing out the classic DIR in reverse order (slice-selective inversionimmediately followed by a non-selective inversion) will work better.This is not the classic DIR preparation but most likely patent protectedalready.

In more detail, FIG. 9 shows a non-selective IR followed by a timedwait—then a classic DIR—followed by another timed wait—followed by areadout. The non-selective IR inverts the signal of blood, normalmyocardium, and infarct. After this event, the blood, normal myocardium,and infarct signal recovers. A later classic DIR leaves the normalmyocardium and infarct untouched, but selectively inverts the blood. Ifthe correct wait time is chosen, the blood curve and the normalmyocardium curve will cross zero (“be nulled, have dark imageintensity”) at the same time, whereas infarct already has recovered moreand has a positive signal (bright image intensity). That is thetime-point when the data is read out

FIG. 10 shows an exemplary illustrative implementation providing aslice-selective IR—followed by a timed wait—followed by a classicDIR—followed by another wait—followed by a readout. The slice-selectiveIR inverts the signal of normal myocardium and infarct, but leaves theblood untouched. After this event, the normal myocardium, and infarctsignal recovers, blood is still at +M0. A later classic DIR leaves thenormal myocardium and infarct untouched, but selectively inverts theblood. If the correct wait time is chosen, the blood curve and thenormal myocardium curve will cross zero (“be nulled, have dark imageintensity”) at the same time, whereas infarct already has recovered moreand has a positive signal (bright image intensity). The time fromclassic DIR to data readout is longer than in idea A making it morerobust.

Note that in both FIG. 9 and FIG. 10, the first preparation pulse isplayed in the diastole of the previous heartbeat. This ensures that theclassic DIR preparation is played early enough so that fresh blood canenter the imaged slice before the data readout. Otherwise blood wouldnot appear black in the image (There would still be blood hanging aroundin the imaged slice that saw the slice-selective preparations).

A potential disadvantage of the FIGS. 9 and 10 pulse sequences is thatthey may be less robust than the previous ones due to a smaller “waitagain” time (see figures) between the selective prep part of the classicDIR* and the data readout. However, we expect the FIG. 10 pulse sequenceto be robust enough, and possibly more robust than the FIG. 9 pulsesequence.

Example Imaging Results

FIGS. 11A and 11B show exemplary imaging results with a dog heart. FIG.11A uses a standard bright blood technique currently used in clinicalpractice. FIG. 11B is an example image of the new black blood approach.

FIGS. 12A and 12B show exemplary imaging results with another dog heart.FIG. 12A uses a standard bright blood technique currently used inclinical practice. FIG. 12B is an example image of the new black bloodapproach.

FIGS. 13A and 13B show exemplary imaging results with another dog heart.FIG. 13A uses a standard bright blood technique currently used inclinical practice. FIG. 13B is an example image of the new black bloodapproach.

FIGS. 14A and 14B show exemplary imaging results with another dog heart.FIG. 14A uses a standard bright blood technique currently used inclinical practice. FIG. 14B is an example image of the new black bloodapproach.

FIGS. 15A, 15B and 15C show exemplary imaging results for an infarctedhuman heart. FIG. 15A shows a conventional clinical bright bloodapproach. FIGS. 15B and 15C show exemplary images resulting from the newblack blood approach.

FIGS. 16A, 16B and 16C show exemplary imaging results for an infarctedhuman heart. FIG. 16A shows a conventional clinical bright bloodapproach. FIGS. 16B and 16C show exemplary images resulting from the newblack blood approach.

The exemplary illustrative non-limiting technology herein has thecapability of being extremely useful. Such a method has been soughtafter by the cardiac MR community for many years. The visualization ofsubendocardial infarcts would be possible or tremendously facilitated bythis technique. Lives may be saved or extended as a result.

All documents cited herein are hereby incorporated by reference as ifexpressly set forth.

While the technology herein has been described in connection withexemplary illustrative non-limiting embodiments, the invention is not tobe limited by the disclosure. The invention is intended to be defined bythe claims and to cover all corresponding and equivalent arrangementswhether or not specifically disclosed herein.

1. A magnetic resonance imaging method comprising: applying aslice-selective inversion NMR pulse to a patient, then waiting a firstcalculated wait time, then applying a non-selective inversion NMR pulseto the patient, then waiting a second wait time calculated so that theblood curve and the normal myocardium curve will cross zero at the sametime whereas infarct already has recovered more and has a positivesignal, then acquiring NMR echoes and generating an image at least inpart based on said acquired NMR echoes, said image showing normal tissueand blood within the patient's heart as the same color or intensity. 2.The method of claim 1 wherein the acquiring comprises using a gradientecho readout.
 3. The method of claim 1 wherein the acquiring comprisesusing a steady-state-free-precession readout.
 4. The method of claim 1wherein the acquiring comprises using a turbo-spin echo readout.
 5. Amagnetic resonance imaging method comprising: applying a slice-selectivesaturation NMR pulse to a patient, then waiting a first calculated waittime, then applying a non-selective inversion NMR pulse to the patient,then waiting a second wait time calculated so that the blood curve andthe normal myocardium curve will cross zero at the same time whereasinfarct already has recovered more and has a positive signal, thenacquiring NMR echoes and generating an image at least in part based onsaid acquired NMR echoes, said image showing normal tissue and bloodwithin the patient's heart as the same color or intensity.
 6. A magneticresonance imaging system comprising: at least one magnet; at least oneRF transmitter and associated coil; an RF receiver; a controller coupledto the RF transmitter and the RF receiver, the controller controllingthe transmitter to apply a slice-selective inversion NMR pulse to apatient, then waiting a first calculated wait time, then applying anon-selective inversion NMR pulse to the patient, then waiting a secondwait time calculated so that the blood curve and the normal myocardiumcurve will cross zero at the same time whereas infarct already hasrecovered more and has a positive signal, the controller thencontrolling the receiver to acquire NMR echoes at the end of the secondcalculated wait time; and an imaging reconstruction processor coupled tothe receiver, the image reconstruction processor processing the acquiredNMR echoes to generate an image based on said acquired NMR echoes, saidimage showing normal tissue and blood within the patient's heart as thesame color or intensity and infarct as a different color or intensity.7. The method of claim 6 wherein image reconstruction processor uses agradient echo readout.
 8. The method of claim 6 wherein the imagereconstruction processor uses a steady-state-free-precession readout. 9.The method of claim 6 wherein the image reconstruction processor uses aturbo-spin echo readout.
 10. A magnetic resonance imaging systemcomprising: at least one magnet; at least one RF transmitter andassociated coil; an RF receiver; a controller coupled to the RFtransmitter and the RF receiver, the controller controlling thetransmitter to apply a slice-selective saturation NMR pulse to apatient, then waiting a first calculated wait time, then applying anon-selective inversion NMR pulse to the patient, then waiting a secondwait time calculated so that the blood curve and the normal myocardiumcurve will cross zero at the same time whereas infarct already hasrecovered more and has a positive signal, the controller thencontrolling the receiver to acquire NMR echoes at the end of the secondcalculated wait time; and an imaging reconstruction processor coupled tothe receiver, the image reconstruction processor processing the acquiredNMR echoes to generate an image based on said acquired NMR echoes, saidimage showing normal tissue and blood within the patient's heart as thesame color or intensity and infarct as a different color or intensity.11. In a magnetic resonance imaging system comprising at least onemagnet; at least one RF transmitter and associated coil, an RF receiver,and a controller coupled to the RF transmitter and the RF receiver, andan imaging reconstruction processor coupled to the receiver, the imagereconstruction processor processing the acquired NMR echoes to generatean image based on said acquired NMR echoes, said image showing normaltissue and blood within the patient's heart as the same color orintensity and infarct as a different color or intensity, anon-transitory storage device associated with the controller that storesinstructions controlling the transmitter to apply a slice-selectiveinversion NMR pulse to a patient, then waiting a first calculated waittime, then applying a non-selective inversion NMR pulse to the patient,then waiting a second wait time calculated so that the blood curve andthe normal myocardium curve will cross zero at the same time whereasinfarct already has recovered more and has a positive signal, theinstructions then controlling the receiver to acquire NMR echoes at theend of the second calculated wait time.
 12. In a magnetic resonanceimaging system comprising at least one magnet; at least one RFtransmitter and associated coil, an RF receiver, and a controllercoupled to the RF transmitter and the RF receiver, and an imagingreconstruction processor coupled to the receiver, the imagereconstruction processor processing the acquired NMR echoes to generatean image based on said acquired NMR echoes, said image showing normaltissue and blood within the patient's heart as the same color orintensity and infarct as a different color or intensity, anon-transitory storage device associated with the controller that storesinstructions controlling the transmitter to apply a slice-selectivesaturation NMR pulse to a patient, then waiting a first calculated waittime, then applying a non-selective inversion NMR pulse to the patient,then waiting a second wait time calculated so that the blood curve andthe normal myocardium curve will cross zero at the same time whereasinfarct already has recovered more and has a positive signal, theinstructions then controlling the receiver to acquire NMR echoes at theend of the second calculated wait time.